A High Pressure Feeder (xe2x80x9cHPFxe2x80x9d) is an commonly used device to process comminuted cellulosic fibrous material, such as wood chips, to produce cellulose pulp. An exemplary HPF is shown in U.S. Pat. No. 5,236,285. The HPF is a pressure interface device between a low pressure stream and a high pressure stream, whereby fibrous material in the low pressure stream can be injected into the high pressure stream that may feed to a pressurized vessel, such as a digester. The HPF may be a rotary valve-type device that, with the aid of a high-pressure pump, transfers a slurry of material and liquid at a low pressure for example, between about 0 to 2 bar gauge, to a second higher pressure, for example, between about 5-15 bar gauge.
The high pressure slurry flow passing through a HPF applies large forces to the components, housings and joints within the HPF. High pressure feeders are designed to withstand these large pressures. However, if the high pressures are applied unequally within the HPF, there is a danger that a large pressure differential can damage the HPF. Equalizing the pressures on the rotor in the HPF is one technique used to enable the HPF to withstand internal high pressures.
Within a HPF, the ends of rotors is one area that has to withstand high pressures. Under conventional operation, the pressures acting on the opposite ends of the rotor are equalized by an external pipe mounted to the HPF housing. Equalized pressure balances the pressure forces acting on opposite ends of the rotor. However, if the pressure on one end of the rotor is substantially higher than the pressure on the opposite end, the unequal forces acting on the rotor ends press the rotor axially against the HPF housing. These axial rotor forces can damage the rotor, the bearings supporting the rotor, and the HPF housing. In extreme cases, the axial pressures may cause the rotor to burst out an end of the HPF housing.
Traditionally, a pressure equalization pipe has been installed in a HPF to ensure that the pressure at both ends of the rotor is equalized. The pressure equalization pipe couples one end of the rotor housing to the other, and spans the length of the housing. The pressure equalization pipe is external to the HPF housing and must be added to the housing during assembly of the HPF. The pressure equalization pipe is prone to damage, exposed to weather, is subject to tampering, and is an additional component that increases the expense of a HPF. In view of these shortcomings of an external pressure equalization pipe, there is a long-felt need for a means to ensure pressure equalization around the rotor of a HPF that does not require the external components of the conventional pressure equalization pipe.
A conduit extends laterally through a rotor of a HPF to relieve any unequal pressures acting on opposite ends of the rotor. The conduit allows slurry under extraordinarily high pressure at one end of the rotor, to flow laterally through the rotor, and be released through the opposite end of the rotor into the rotor housing.
In one embodiment, the invention is a high pressure transfer device comprising: a pocketed rotor containing a plurality of through going pockets, said rotor rotatable about a given axis of rotation and said pockets having opposite end openings which function as both inlets and outlets depending upon the angular position of the rotor and said pockets are provided in at least first and second sets; a housing enclosing said rotor and having an exterior periphery and first through fourth ports disposed around the exterior periphery thereof for registry with the inlets to and outlets from said through going pockets, wherein the rotor is mounted in said housing for rotation with respect to said ports about said given axis of rotation; and said rotor having at least one conduit extending axially through the rotor and having openings at opposite ends of said rotor to provide pressure equalization at said opposite ends.
In a second embodiment, the invention is a high pressure transfer device comprising: a pocketed rotor containing a plurality of through going pockets, said rotor rotatable about a given axis of rotation and said pockets having opposite end openings which function as both inlets and outlets depending upon the angular position of the rotor; a housing enclosing said rotor having first through fourth ports disposed around the exterior periphery thereof for registry with the inlets to and outlets from said through going pockets; said rotor mounted in said housing for rotation with respect to said ports about said given axis of rotation; and said rotor having end plates at opposite axial ends of said rotor, wherein said end plates have at least one slot open to a conduit extending axially through said rotor, such that said at least one slot in said end plates and said conduit provide pressure equalization between said axial ends of the rotor.